ORIGINAL: britbrat
ORIGINAL: 2slow2matter
ball bearings--support the crankshaft. Most have them at the front and back--this is the best setup. The other alternative is a bushing--basically a polished metal to metal point of contact--much more friction using this setup than with ball bearings--therefore, the ball bearing engines aren't robbed of as much power as the bushing engines are. ---
There is no metal-metal contact with a bushing engine. The crank "floats" on a film of lubricant within the journal (bushing) bearing & has very low friction. The reason BB engines are generally more powerfull is that they invariably have larger & more agressively timed inlet & exhaust ports. Bushing bearings are cheaper to make & are therefore used on low end engines that are primarily employed as "trainer" engines. These can last every bit as long as a BB engine & in some cases are as powerfull as their BB counterparts.
Brit,
that is exactly what a bushing is--two pieces of polished metal that ride next to each other. Yes, you are correct, there is a thin film of lubricant that coats these surfaces and this reduces the friction, but does not eliminate friction. Friction cannot be eliminated. When first started, or if ran lean, that film of lubricant can be very thin, or non-existant. Therefore, in my experience (and I have both kinds of engines) bushing engines need to be ran a little richer than ball bearing engines. At least that's according to my OS manuals.
I stand by my assumption that ball bearing engines are much stronger than their bushing counterparts. However, both have their places.
That being said, I would not even consider a bushing engine in this application.
My opinion is quit killing yourself over this decision, and order the 50 SX. You'll be happier in the end, and never question what if. A couple of reasons for this:
first and foremost--it's what you want
second--it will power your second plane much better, and it sounds like you'll be moving on pretty quickly
Third--it's probably more for your money.
I do not have any experience with ringed two stroke engines, but if it's an OS, it's good.
I have two brands of two stroke engines--evolution, and OS. I routinely go to the field to see other modlers tinkering with their engines, while I fly. My brother had a super tiger engine that he eventually quit fiddling with--nothing but a headache. I'm sure some people have no problems with it, but personal preference--I like flying more than tinkering. I had a VMAX engine that I tried--second flight it broke the con-rod. I got it replaced and promptly sold it to my dad for 45 dollars. I've never looked back, and neither has he (lots of successful flights on it so far). I'll never own another one, and he probably would. So, to each his own. HOwever, I'm with piper on this one--if you want reliability, go with the OS (or evolution).